resolv.conf appears incorrect upon reboot

[Emre ISIK <eis@sci.akdeniz.edu.tr>]

After my internet access had problems, I realised that IP numbers were 
accepted, while internet addresses were not. I've realised that my 
/etc/resolv.conf had changed to have a different (perhaps default) DNS 
number (172.20.0.1) than the one I had set during the first 
installation. When I change it by hand, I access everyhwere. But when I 
reboot the system, it takes the same DNS number again. Lastly, how can I 
reconfigure my network settings using debconf (I mean dpkg-reconfigure 
?what?)? Can anyone help me? I "live" in a LAN which uses a DHCP server.

Emre Isik - PhD student in astrophysics...Antalya, Turkey